1. Technical Field
This invention relates generally to a device for unloading catalyst from a tubular reactor, and more particularly to such a device that has an air lance that is mounted on a motor-driven reel.
2. Background Art
Difficulties have been encountered in removing catalyst, such as granular or particulate catalyst, from the tubes of multi-tube reactors. The catalyst is prone to becoming lodged within the tubes during reactor operation. Often, the particulate catalyst may completely block or bridge some or all of the tubes of the reactor due to heat or composition changes during operation, resulting in retarded or blocked movement or flow of the catalyst.
U.S. Pat. No. 5,228,484, issued Jul. 20, 1993 to Kelly J. Johnson, and entitled Air Lance Reel for Catalyst Unloading of Tubular Reactors, describes a device having an air lance that is insertable into catalyst tubes and supplies air for breaking up the catalyst prior to removal. The Johnson device uses an air-motor powered reel to dispense and retrieve the lance from the catalyst tubes of the reactor.
In actual operation, air-motor powered air lance reels have presented several problems. Because the air-powered reel uses a compressible fluid, the reel is subject to retarded start and stop operation and therefore lacks a positive on/off control. Also, as a result of compressed air fluctuations, constant speed control of the reel is difficult to maintain. In addition, when paying out the air lance from the reel, the air-motor driven reel is in a freewheeling mode and the air hose is subject to entanglement. Most importantly, it is essential that no lubricant be introduced into the air stream which could irreparably contaminate the catalyst and cause damage to the reactor itself. Air motors, without lubrication, experience excessive wear and resultant short service life. If the air motor is lubricated, lubricant may escape past seals and enter the air stream with catastrophic consequences.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a device for unloading catalyst material from reactor tubes that has positive on/off motion control so that the nozzle end of an air lance can be precisely positioned within a reactor tube. It is also desirable to have such a device that has a constant speed so that the withdrawal of the air lance from the reactor tube can be accurately controlled. It is also desirable to have such a device wherein the reel on which the air lance hose is wound is retarded, or lightly braked, during the withdrawal of the hose from the reactor and entanglement of the hose due to freewheeling, is avoided. Moreover, it is extremely desirable to have such a device that is powered in such a manner as to avoid the introduction of lubricant into the air stream without adversely affecting the service life of the motor controlling the rotation of the hose reel.